Fluid flow sensor and low flow cut-off device

ABSTRACT

The present disclosure provides a fluid flow sensor and low flow cut-off device and an associated method for its operation that is easily integrated into a fluid delivery and/or fluid control system for a variety of appliances, such as boilers and water heaters. The fluid flow sensor and low flow cut-off device can determine a fluid flow rate in or to an appliance and whether that fluid flow rate meets or exceeds a predetermined fluid flow rate threshold for the safe and/or efficient operation of the appliance and, if the threshold is not met, disable the appliance from operating or continuing to operate under such conditions.

FIELD

The present disclosure relates to a fluid flow sensor and low flowcut-off device for boiler or water heater systems and an associatedmethod of operation.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Conventional boilers and water heater systems include a cut-off devicethat is intended to interrupt the operation of the boiler or waterheater to prevent damage to the system in the event that water flow inor to the boiler or water heater falls below a predetermined minimumflow rate required for the safe and/or efficient operation of theappliance. Such conventional low flow cut-off devices have a mechanicaldesign configuration associated with a switch having relay contacts thatopen or close to disable/enable the operation of a burner for the boileror water heater. In the event of a low flow condition, the relaycontacts open and prevent the burner from turning ON or continuing torun.

Such conventional electro-mechanical low flow cut-off devices, however,exhibit less than desirable operating life spans. Moreover, the devicesdo not provide a continuous signal indicative of the fluid flow rate asfeedback into a system controller for enabling/disabling operation ofthe burner. Consequently, in certain instances there is a potential forthe device to latch in a given state even though the fluid flow rate mayhave changed. In addition, the device includes multiple separatecomponents and does not comprise an integrated device. As such, thereexists a need for an improved low flow cut-off device for a water heateror boiler systems.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A fluid flow sensor and low flow cut-off device for an appliance isdisclosed as including a probe disposed at a fluid supply to theappliance, a first control unit in electrical communication with theprobe, and a second control unit in electrical communication with thefirst control unit and the appliance.

The probe is operable to generate an output signal indicative of a fluidflow rate to the appliance.

The first control unit monitors the output signal and determines thefluid flow rate over time. The fluid flow rate is compared to apredetermined threshold fluid flow rate at a first time. If the fluidflow rate is greater than or equal to the predetermined threshold fluidflow rate, the first control unit generates a first safety signaloutput. The first control unit also compares the fluid flow rate to thepredetermined threshold fluid flow rate at a second time. If the fluidflow rate at the second is greater than or equal to the predeterminedthreshold fluid flow rate, the first control unit generates a secondsafety signal output.

In another aspect of the disclosure, the first control unit monitors theoutput signal and determines a fluid flow rate over time, and comparesthe fluid flow rate to a predetermined threshold fluid flow rate andsimultaneously generates both a first safety signal output and a secondsafety signal output if the fluid flow rate is greater than or equal tothe predetermined threshold fluid flow rate.

The second control unit includes a switch that is operable to enableoperation of the appliance. The switch has a first switch interface anda second switch interface. The first safety signal output is received atthe first switch interface and the second safety signal is received atthe second switch interface. Only when both the first and second safetysignal outputs are received, respectively, at the first and secondswitch interfaces, however, does the switch enable operation of theappliance.

In another aspect of the disclosure, one of the first and the secondsafety signal outputs can be a constant signal and the other of thefirst and the second safety signal outputs can be a pulsed signal. Theswitch can comprise a relay having a normally-opened condition, thefirst switch interface can comprise a high-side control for the relay,and the second switch interface can comprise a low-side control for therelay, and one of the first and second switch interfaces can comprise apulse detector circuit, such as resistor-capacitor (R-C) circuit.Alternatively, both the first and the second safety signal outputs canbe a pulsed signal and both the first and second switch interfaces cancomprise a pulse detector circuit.

The fluid flow sensor and low flow cut-off device for an appliance ofthe disclosure can be operable to enable operation of a burner for andappliance like a boiler or a water heater.

In another aspect of the disclosure, a method for controlling theoperation of an appliance is provided. The method includes determining afirst fluid flow rate at the appliance at a first time, comparing thefirst fluid flow rate to a threshold fluid flow rate, and generating afirst safety signal if the first fluid flow rate is greater than orequal to the threshold fluid flow rate. In addition, the method includesdetermining a second fluid flow rate at the appliance at a second time,comparing the second fluid flow rate to the threshold fluid flow rate,and generating a second safety signal if the second fluid flow rate isgreater than or equal to the threshold fluid flow rate. The first safetysignal is communicated to and/or received by a high-side of a switch forenabling operation of the appliance. The second safety signal iscommunicated to and/or received by a low-side of the switch. The switchis closed only when both the first safety signal and the second safetysignal are communicated to the switch, thereby enabling operation of theappliance.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

The present disclosure will become more fully understood from thedetailed description and the accompanying drawing, wherein:

FIG. 1 is a schematic block diagram of a fluid flow sensor and low flowcut-off device according to the present disclosure;

FIGS. 2A and 2B show block diagrams of a fluid flow sensor and low flowcut-off device according to the present disclosure having alternativeconfigurations; and

FIG. 3 is a flow chart describing the operation of a fluid flow sensorand low flow cut-off device according to the present disclosure.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. The example embodiments will now be described more fullywith reference to the accompanying drawings.

The present disclosure provides a fluid flow sensor and low flow cut-offdevice 1 and an associated method for its operation that is easilyintegrated into a fluid delivery and/or fluid control system for avariety of appliances, such as boilers and water heaters. The fluid flowsensor and low flow cut-off device 1 of the present disclosure candetermine a fluid flow rate F in or to an appliance and whether thatfluid flow rate F meets or exceeds a predetermined fluid flow ratethreshold F_(t) for the safe and/or efficient operation of the applianceand, if the threshold is not met, disable the appliance from operatingor continuing to operate under such conditions.

FIG. 1 generally depicts the major components of the fluid flow sensorand low flow cut-off device 1 in accordance with the present disclosure.The device 1 includes a fluid flow rate sensor 10 for detecting the flowof a fluid (e.g., water) in or to an appliance 12 (e.g., a boiler orwater heater) and an appliance cut-off switch 14 for disabling theoperation of the appliance 12 in the event of a low fluid flowcondition. When the fluid flow rate in or to the appliance 12 is greaterthan or equal to a requisite threshold flow rate that is needed for thesafe and/or efficient operation of the appliance, e.g., a predeterminedthreshold fluid flow rate F_(t), the fluid flow rate sensor 10 generatesand sends redundant (e.g., at least two) digital safety signal outputs,first safety signal output 16 and second safety signal output 18, thatare indicative of a positive flow condition. The first and second safetysignal outputs 16, 18 are transmitted to the appliance cut-off switch 14and enable operation of the appliance 12. As described with respect tothe exemplary embodiment disclosed herein, operation of the appliance 12is enabled only when both the first and second safety signal outputs 16,18 are generated and sent to the cut-off switch 14 to indicate apositive flow condition.

The fluid flow rate sensor 10 is of the thermo-anemometer-type andcontains no moving parts. The fluid flow rate sensor 10 includes a probe20 and a first control unit 22. In use, the probe 20 is disposed at orwithin the fluid supply of the appliance 12, for example, and issubjected to the flow of fluid leading to the appliance 12. Whensubjected to fluid flow, the probe 20 experiences a change in conditionand can produce an output signal 24 (e.g., a voltage) that is indicativeof a fluid flow rate F. The features, functions and methods associatedwith operating the fluid flow rate sensor 10 and determining a fluidflow rate F and other conditions (e.g., temperature of the fluid) aregenerally known. For example, such a sensor is shown and described inU.S. Pat. No. 7,685,875, entitled “Fluid Flow Rate Sensor and Method ofOperation,” issued Mar. 30, 2010 and in U.S. Pat. No. 7,333,899,entitled “Fluid Flow Rate Sensor and Method of Operation,” issued Feb.19, 2008, both owned by Therm-O-Disc, Incorporated, the assignee of thepresent patent application, the disclosures of which are both herebyincorporated in their entirety by reference.

Referring again to FIG. 1, the fluid flow rate sensor 10 includes afirst control unit 22 in electrical communication with the probe 20. Thefirst control unit 22 communicates with and controls the operation ofthe probe 20. The first control unit 22 can determine the fluid flowrate F and the temperature T of the fluid in a well-known manner, forexample, and provide one or more outputs representative of thoseconditions. The fluid flow rate F and other conditions can becontinuously or intermittently monitored and determined by the fluidflow rate sensor 10 over time. For example, at time=t_(n), a fluid flowrate F_(n) can be determined, thereafter at time=t_(n+1), a fluid flowrate F_(n+1) can be determined, and so on.

In addition, the first control unit 22 can perform comparisons of thedetermined fluid flow rate F against a predetermined threshold fluidflow rate F_(t) over time. Based on the comparisons, the first controlunit 22 can generate one or more of the digital safety signal outputs16, 18. For example, the first control unit 22 can compare the fluidflow rate F_(n) to the predetermined threshold flow rate at time=t_(n).If the fluid flow rate F_(n) is greater than or equal to thepredetermined threshold F_(t), then the first control unit 22 cangenerate one of the first or second digital safety signal outputs 16,18. Thereafter, at time=t_(n+1), the first control unit can compare thefluid flow rate F_(n+1) to the predetermined threshold fluid flow rateF_(t). Similarly, if the fluid flow rate F_(n+1) is greater than orequal to the predetermined threshold F_(t), then the first control unit22 can generate the other of the first or second digital safety signaloutputs 16, 18. If the comparisons determine that either fluid flow rateF_(n) and/or F_(n+1) is less than the predetermined threshold F_(t),then the first control unit 22 does not generate the first safety signaloutput 16 and/or the second safety signal output 18. In an alternativeexample, the first control unit 22 can simultaneously generate (and/orregenerate) both the first safety signal output 16 and the second safetysignal output 18 each time (e.g., t_(n), t_(n+1), t_(n+2), etc.) thefirst control unit 22 conducts a comparison of the fluid flow rate(e.g., F_(n), F_(n+1), F_(n+2), etc.) to the predetermined thresholdF_(t) flow rate and the fluid flow rate F is greater than or equal tothe predetermined threshold F_(t).

Also as shown in FIG. 1, a second control unit 24 can be included in thefluid flow sensor and low flow cut-off device 1. The second control unit24 is electrically connected to the first control unit 22. The secondcontrol unit 24 can include an electrically-operated switch or relay 36that is normally open. As shown in FIG. 1, the relay 36 has a firstswitch interface 32, e.g., a high side control switch for the relay 36,and a second switch interface 34, e.g., a low side control switch forthe relay 36 that are electrically in series with the relay 36. Thefirst and second safety signal outputs 16, 18 generated and sent by thefirst control unit 22 are received in the second control unit 24,respectively at the first and second switch interfaces 32, 34. When boththe first switch interface 32 and the second switch interface 34 areclosed, the relay 36 switches to a closed condition and the appliance 12is operable (e.g., the burner is ENABLED). If either of the first switchinterface 32 or second switch interface 34 is open, however, the relay36 switches to or remains in an open condition and the appliance 12 isnot operable (e.g., the burner is DISABLED).

In alternative configurations shown in FIGS. 2A and 2B, however,although still electrically in series with the relay 36, both the firstswitch interface 32 and the second switch interface 34 can together formeither a high-side control for the relay 36 (FIG. 2A) or a low-sidecontrol for the relay 36 (FIG. 2B). In either alternative configuration,though, if either of the first switch interface 32 or second switchinterface 34 is open, however, the relay 36 switches to or remains in anopen condition and the appliance 12 is not operable (e.g., the burner isDISABLED).

Operation of an exemplary fluid flow sensor and low flow cut-off device1 can be understood with reference to FIGS. 1 and 3. The fluid flow ratesensor 10 can determine the fluid flow rate F in or to the appliance 12continuously or at regular intervals in a manner well-known anddescribed in U.S. Pat. No. 7,685,875, entitled “Fluid Flow Rate Sensorand Method of Operation,” issued Mar. 30, 2010. At time=t_(n), the fluidflow rate F_(n) is compared against the predetermined threshold flowrate value F_(t). If the fluid flow rate F_(n) is greater than or equalto the predetermined threshold flow rate value F_(t), then the firstcontrol unit 22 can generate the first safety signal 16 which iscommunicated to the first switch interface 32. When received at thefirst switch interface 32, the first safety signal 16 causes the highside control switch for the relay 36 to close.

Thereafter, at time=t_(n+1), the fluid flow rate F_(n+1) is comparedagainst the predetermined threshold flow rate value F_(t). If the fluidflow rate F_(n+1) is greater than or equal to the predeterminedthreshold flow rate value F_(t), then the first control unit 22 cangenerate the second safety signal 18. The second safety signal 18 iscommunicated to the second switch interface 34. When received at thesecond switch interface 34, the second safety signal 18 causes the lowside control switch for the relay 36 to close.

Consequently, if the first safety signal 16 is not generated by thefirst control unit 22, then no signal is sent to the high-side control32 of the relay 36 and the relay 36 remains in its normally opencondition. Similarly, if the second safety signal 18 is not generated bythe first control unit 22, then no signal is sent the low side control34 of the relay 36 and the relay 36 remains in its normally opencondition. In either situation, the appliance 12 is not operable (e.g.,the burner is DISABLED). If both the first switch interface 32 and thesecond switch interface 34 are closed, however, then the relay 36 iscaused to be closed and the appliance 12 is operable (e.g., the burneris ENABLED). The appliance can then safely and/or efficiently beoperated and/or continue to operate without the risk of damage to theappliance due to a low fluid flow condition. Moreover, it can beappreciated that the alternative configurations shown in FIGS. 2A and 2Blikewise function in a similar manner, necessitating that both the firstswitch interface 32 and the second switch interface 34 must respectivelyreceive the first and second safety signals 16, 18 in order to cause therelay 36 to close or remain closed.

At least one of the first safety signal 16 and second safety signal 18can be a pulsed signal (i.e. voltage) delivered to its respective switchinterface 32, 34, and the other of the first safety signal 16 and secondsafety signal 18 can be a constant signal delivered to its respectiveswitch interface 32, 34. In addition, at least one of the first switchinterface 32 and second switch interface 34 can be pulse detectorcircuit, such as a resistor-capacitor (R-C) circuit, that receives thepulsed safety signal. If the pulsed safety signal is not periodicallysent to the R-C circuit switch interface, then the R-C circuit no longerstays closed and the relay 36 returns to its normally open condition,thereby disabling the appliance 12. For the purposes of the exemplaryembodiment described in this disclosure, the first safety signal 16 is aconstant signal received at the first switch interface 32 and the secondsafety signal 18 is a pulsed signal received at the second switchinterface 34. However, it can be understood that both the first andsecond safety signals 16, 18 can also be pulsed signals.

Because the first control unit 22 can conduct multiple, comparisonsbetween the fluid flow rates F_(n) and F_(n+1) determined over time,such as times t_(n) and t_(n+1), with the predetermined threshold flowrate value F_(t), and because the results of those comparisons must bothindicate a positive flow condition (i.e., the fluid flow rate is greaterthan or equal to the predetermined threshold fluid flow rate) in orderfor the appliance 12 to be operable, the fluid flow sensor and low flowcut-off device 1 provides a failsafe protection against operation of theappliance 12 under conditions where fluid flow in or to the appliance isbelow that which is required for the safe and/or efficient operation ofthe appliance. For example, even if one of the first safety signal 16and second safety signal 18 represents a false positive regardingsufficient fluid flow, the absence of the other of the first and secondsafety signals 16, 18 can still prevent operation of the appliance.Therefore, the risk that a hardware and/or software fault could producean incorrect or false signal regarding the flow of fluid F through thesystem, and maintain the appliance in an operable state when theappliance should, instead, be disabled, is reduced.

Consequently, even if a hardware fault or the like causes a falseindication of a positive flow condition and one of the safety signaloutputs 16, 18 is erroneously generated and sent by the fluid flow ratesensor 10 to the cut-off switch 14, the absence of the redundant safetysignal output(s) 16, 18 can prevent operation of the appliance 12.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A fluid flow sensor and low flow cut-off devicefor an appliance comprising: a probe disposed at a fluid supply to theappliance; a first control unit in electrical communication with theprobe; and a second control unit in electrical communication with thefirst control unit and the appliance; wherein the probe generates anoutput signal indicative of a fluid flow rate to the appliance; whereinthe first control unit monitors the output signal and determines thefluid flow rate over time and compares the fluid flow rate to apredetermined threshold fluid flow rate at a first time, and generates afirst safety signal output if the fluid flow rate is greater than orequal to the predetermined threshold fluid flow rate, and compares thefluid flow rate to the predetermined threshold fluid flow rate at asecond time and generates a second safety signal output if the fluidflow rate is greater than or equal to the predetermined threshold fluidflow rate; wherein the second control unit comprises a switch operableto enable operation of the appliance, the switch having a first switchinterface and a second switch interface, wherein the first safety signaloutput is received at the first switch interface and the second safetysignal is received at the second switch interface; and wherein only whenboth the first and second safety signal outputs are received,respectively, at the first and second switch interfaces does the switchenable operation of the appliance.
 2. The fluid flow sensor and low flowcut-off device for an appliance of claim 1 wherein at least one of thefirst and the second safety signal outputs is a pulsed signal; andwherein at least one of the first and second switch interfaces comprisesa pulse detector circuit.
 3. The fluid flow sensor and low flow cut-offdevice for an appliance of claim 2 wherein the at least one of the firstand second switch interfaces that comprises a pulse detector circuit isa resistor-capacitor circuit.
 4. The fluid flow sensor and low flowcut-off device for an appliance of claim 2 wherein the switch comprisesa relay having a normally-opened condition; and wherein the first switchinterface and the second switch interface are electrically in serieswith the relay.
 5. The fluid flow sensor and low flow cut-off device foran appliance of claim 4 wherein the first switch interface comprises ahigh-side control for the relay, and the second switch interfacecomprises a low-side control for the relay.
 6. The fluid flow sensor andlow flow cut-off device for an appliance of claim 4 wherein the firstswitch interface and the second switch interface are electrically inseries with one another and together comprise either a high-side controlor a low-side control for the relay.
 7. The fluid flow sensor and lowflow cut-off device for an appliance of claim 1 wherein the appliance isa boiler or a water heater and the switch is operable to enableoperation of a burner for the appliance.
 8. A method for controlling theoperation of an appliance, the method comprising: determining a firstfluid flow rate at the appliance at a first time; comparing the firstfluid flow rate to a threshold fluid flow rate; generating a firstsafety signal if the first fluid flow rate is greater than or equal tothe threshold fluid flow rate; determining a second fluid flow rate atthe appliance at a second time; comparing the second fluid flow rate tothe threshold fluid flow rate; generating a second safety signal if thesecond fluid flow rate is greater than or equal to the threshold fluidflow rate; communicating the first safety signal to a high-side of aswitch for enabling operation of the appliance; communicating the secondsafety signal to a low-side of the switch; closing the switch only whenboth the first safety signal and the second safety signal arecommunicated to the switch; and enabling operation of the appliance. 9.A fluid flow sensor and low flow cut-off device for an appliancecomprising: a probe disposed at a fluid supply to the appliance; a firstcontrol unit in electrical communication with the probe; and a secondcontrol unit in electrical communication with the first control unit andthe appliance; wherein the probe generates an output signal indicativeof a fluid flow rate to the appliance; wherein the first control unitmonitors the output signal and determines a fluid flow rate over timeand compares the fluid flow rate to a predetermined threshold fluid flowrate, and simultaneously generates both a first safety signal output anda second safety signal output if the fluid flow rate is greater than orequal to the predetermined threshold fluid flow rate; wherein the secondcontrol unit comprises a switch operable to enable operation of theappliance, the switch having a first switch interface and a secondswitch interface, wherein the first safety signal output is received atthe first switch interface and the second safety signal is received atthe second switch interface; and wherein only when both the first andsecond safety signal outputs are received, respectively, at the firstand second switch interfaces does the switch enable operation of theappliance.
 10. The fluid flow sensor and low flow cut-off device for anappliance of claim 9 wherein at least one of the first and the secondsafety signal outputs is a pulsed signal; and wherein at least one ofthe first and second switch interfaces comprises a pulse detectorcircuit.
 11. The fluid flow sensor and low flow cut-off device for anappliance of claim 10 wherein the at least one of the first and secondswitch interfaces that comprises a pulse detector circuit is aresistor-capacitor circuit.
 12. The fluid flow sensor and low flowcut-off device for an appliance of claim 10 wherein the switch comprisesa relay having a normally-opened condition; and wherein the first switchinterface and the second switch interface are electrically in serieswith the relay.
 13. The fluid flow sensor and low flow cut-off devicefor an appliance of claim 12 wherein the first switch interfacecomprises a high-side control for the relay, and the second switchinterface comprises a low-side control for the relay.
 14. The fluid flowsensor and low flow cut-off device for an appliance of claim 12 whereinthe first switch interface and the second switch interface areelectrically in series with one another and together comprise either ahigh-side control or a low-side control for the relay.
 15. The fluidflow sensor and low flow cut-off device for an appliance of claim 9wherein the appliance is a boiler or a water heater and the switch isoperable to enable operation of a burner for the appliance.